Edexcel Chemistry A Level: Guide Questions with Complete Answers. Verified for New Updates

Mass spectrometry using lasers to ionise atoms into cations, then measure the abundance and mass using their mass-tocharge ratios Mass to charge ratio the mass of an ion divided by its charge (usually +1 in mass spectrometry) units: m/z relative atomic mass the average mass of an atom of an element relative to 1/12 of an atom of the isotope C-12 relative isotopic mass the relative mass an atom of an isotope relative to 1/12 of the mass of a C-12 atom relative molecular mass the relative mass of a molecule, differs due to different isotopes of the atoms in the molecule relative formula mass the average mass the atoms within a unit, used with large ionic compounds where there are more atoms than given in the chemical formula avogadros constant the number of particles in 1 mole: 6.02 * 10^23 empirical formula the simplest ratio of elements in a compoud percentage composition the percentage by mass of each element in a compound gas laws show how the volume of a gas depends on 3 things: - temperature (T) - pressure (p) - quantity of gas in moles (n) ideal gas a hypothetical gas that perfectly obeys all of the gas laws ideal gas equation pV=nRT value of R in ideal gas equation 8.31 (the gas constant) Principal quantum number the main energy level of an electron (n) First Ionisation Energy the energy required to remove 1 electron from each gaseous atom in 1 mole of atoms to become +1 gaseous cations First Ionisation Energy Equation (using element Z) Z(g) --> Z+1(g) + e-1 Second Ionisation Energy energy required to remove 1 electron from each +1 cation in 1 mole of gaseous ions so each becomes +2 gaseous cations Periodicity trend in element properties with increasing atomic number in a period Shielding a decrease in the nuclear charge experienced by electrons caused by electron-electron repulsion between electron shells Exceptions to Aufbau Principle chromium (4s1 3d5) and copper (4s1 3d10) Isotope atoms of the same element with the same number of protons but a different number of neutrons, meaning they have the same atomic number but different masss numbers VSEPR Theory Valence, Shell, Electrons, Pair, Repulsion Isoelectronic molecules and ions with exactly the same number and arrangement of electrons Linear bond angle 180 Trigonal Planar bond angle 120 V-shaped bond angle (3 electron pairs